Light-based non-invasive blood pressure systems and methods

ABSTRACT

Light-based non-invasive blood pressure measurement systems and methods that include a sensor having a light emitter and a light detector are disclosed. The light emitter emitting coherent or non-coherent light that is transmitted into and reflected from the tissues of the patient, including reflecting from moving blood. The light reflected from the moving blood being having a Doppler shift and detected by the light detector to generate a non-invasive blood pressure signal. The non-invasive blood pressure signal is processed to determine the instantaneous velocity of the blood. Additionally, pulse wave velocity data is obtained nearly, or substantially, simultaneously with the acquisition of the non-invasive blood pressure signal. Using the pulse wave velocity, the instantaneous velocity of the blood and a density of the blood, an instantaneous blood pressure can be determined.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of and priority to U.S.Provisional Patent Application Ser. No. 62/577,982, filed on Oct. 27,2017, entitled “LIGHT-BASED NON-INVASIVE BLOOD PRESSURE,” the contentsof which are hereby incorporated by reference in their entirety.

BACKGROUND

The blood pressure of a patient is a critical measurement that is usedin monitoring and treating the patient. There are two means by which theblood pressure of the patient can be measured, one is invasive and theother is non-invasive. In the invasive means, the blood pressure isobtained by direct measurement, requiring a sensor to be inserted intothe circulatory system of the patient to obtain the measurements. Assuch, the invasive means, while providing an accurate measurement, cancause discomfort in the patient or the subject for which the bloodpressure is being measured. Additionally, there is an increased risk ofcomplications and/or expense due to the invasive nature of such bloodpressure measurement. Such increased complications risk and/or expensescan be unwarranted in many cases, such as during a simple patientexamination.

In the non-invasive means, the sensing of the blood pressure is doneexternally to the patient. Typically, this involves the application of acuff about a limb of the patient and the pressurization of the cuff tocut-off circulation through the limb. The pressure applied by the cuffto the limb is slowly reduced and as blood flow is resumed, the bloodpressure can be measured based on the pressure remaining in the cuff.This process is often repeated multiple times to ensure an accuratemeasurement or as a means of monitoring over an extended period of time,with pauses required between measurement instances. While this means isnon-invasive, it does require the temporary cessation of circulation ina portion of the patient, which can be damaging to the health of thepatient and also requires time for the process to be fully performed.Additionally, such non-invasive blood pressure measurement techniquesare sensitive to motion of the patient and/or equipment which can resultin inaccurate and/or unobtainable blood pressure measurements. Inpatient transport or emergency situations, the patient and/or apparatuscan be subjected to a large amount of motion during time in which anaccurate blood pressure measurement can be critical to assess the stateof the patient.

Blood pressure measurement and/or monitoring can be improved bynon-invasive blood pressure systems and/or methods that do not requirethe restriction of circulation and provides the accurate blood pressurevalues/measurements needed for patient treatment and/or monitoring,including beat-to-beat blood pressure measurements that areconventionally the domain of invasive means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example light-based non-invasive bloodpressure system.

FIG. 2 is an example light-based non-invasive blood pressure system witha coherent light source.

FIG. 3 is an example light-based non-invasive blood pressure system witha non-coherent light source.

FIG. 4 is an example arrangement of a light-based non-invasive bloodpressure system.

FIG. 5 is an example method of generating a non-invasive blood pressuresignal.

FIG. 6 is an example method of determining a non-invasive bloodpressure.

DETAILED DESCRIPTION

Embodiments of this disclosure measure two values that can be used tocompute a patient's instantaneous blood pressure. Embodiments of thisdisclosure measure the instantaneous Non-Invasive Blood Pressure (NIBP)of a patient with an apparatus that determines the values for, in oneexample, two of the unknowns in the water hammer equation: pulse wavevelocity (PWV) and instantaneous blood velocity (v_(i)). The waterhammer equation relates instantaneous blood pressure to pulse wavevelocity and blood flow velocity as follows:

P_(i)=ρPWV v_(i)

-   -   where PWV is the pulse wave velocity, ρ is the density of the        blood that may be assumed to be a constant, for example, v_(i)        is the instantaneous velocity of the blood, and P_(i) is the        desired instantaneous blood pressure. Other equations relate        instantaneous blood pressure to pulse wave velocity and blood        flow, such as various constitutive equations, like those        described in U.S. patent application Ser. No. 16/103,797, filed        Aug. 14, 2018, titled “CONSTITUTIVE EQUATION FOR NON-INVASIVE        BLOOD PRESSURE MEASUREMENT” and U.S. patent application Ser. No.        15/999,038, filed Aug. 16, 2018, titled “NON-INVASIVE BLOOD        PRESSURE MEASUREMENT DEVICES, SYSTEMS, AND METHODS,” which are        incorporated by reference herein in their entirety. Those other        equations relating instantaneous blood pressure to pulse wave        velocity, blood flow velocity, and/or vessel mechanical        characteristics or geometries may be used in determining the        desired variables using the light-based emitters and detectors        disclosed here.

Some conventional NIBP measurement systems rely on PWV to measure NIBP,but each requires an initial calibration measurement, taken at leastonce, to convert a relative blood pressure value to an actual bloodpressure value. The required calibration measurement is taken using atraditional blood pressure cuff, for example on the arm or perhaps thefinger. Such conventional NIBP measurement systems that require aninitial calibration and all calculations are based on a difference ordifferential value of that initial calibration measurement and aretherefore not an actual measurement of the blood pressure value.

The disclosed NIBP systems and devices instead take an instantaneousblood pressure measurement rather than a change from an initialcalibration measurement. Avoiding the need for a calibration measurementprevents the patient from experiencing blood flow restrictionaltogether. Although PWV is highly correlated with blood pressure (BP)so that changes in blood pressure can be calculated from changes in PWVby relying on an initial calibration measurement relatively accurately,what has not been solved until now is how to eliminate the need toacquire and use a separate, initial calibration value or values toregister a particular PWV to a particular value of blood pressure (asopposed to simply a change in blood pressure) for a patient. State ofthe art of NIBP using PWV typically uses a standard cuff-basedmeasurement, to interrupt the blood flow, to measure and associate aparticular blood pressure to a particular PWV measurement in a patient.Interrupting the blood flow requires that the patient's appendage beingmeasured is compressed to restrict the blood flow. Such restriction ofthe patient's blood flow prevents such conventional methods of measuringblood pressure from being applied to areas of the patient's body thatcannot withstand restricted blood flow, such as a patient's neck, forexample.

In this way, conventional methods and devices that provide NIBPmeasurements using PWV require a distinct calibration step. In contrastto the state of the art, the disclosed embodiments include a method anddevice that eliminate the requirement of a distinct calibration step,especially using a technology that temporarily restricts blood flow. Inshort, the disclosed embodiments include self-calibrating NIBP systemsand methods using PWV, or alternatively, NIBP systems and methods usingPWV without the temporary interruption of blood flow.

The lack of need for a calibration step for devices using the methodtaught herein arises from the use of the approximate relationshipsbetween P_(i), v_(i), and A_(i), such as the water hammer equation inits integrated (non-differential) form. In the water hammer equation,the blood pressure is related to the PWV by a scale factor that can beknown without a distinct calibration step. The scale factor can be foundusing the same ultrasound and/or light-based technology that is used tomeasure the PWV. That scale factor is related to the blood velocity andblood density. In this way, a particular blood pressure is calculated asthe PWV scaled by the blood density and the blood velocity.

Blood velocity can be acquired using light and/or ultrasound as a timevarying waveform. PWV can also be measured with light and/or ultrasoundalso as a time varying function. The time-varying nature of the PWVmeans that it can be updated from beat to beat if desired. Thetime-varying nature of the blood velocity means that blood velocity canbe measured at a much finer resolution than a cardiac cycle, that is tosay, continuously during the cardiac cycle for as many cardiac cycles asis desired. Because blood density is already sufficiently known and isrelatively constant, not only can a particular blood pressuremeasurement be known as if it were obtained by a standard cuff-basedmeasurement, but all manners of blood pressure measurements can be madeas time-varying waveforms describing the instantaneous pressure at asmany points during a cardiac cycle as desired. That is to say, bloodpressure can be monitored continuously throughout the cardiac cycle withas fine a resolution as is required, and this can be done for as manycontiguous cardiac cycles as is desired for beat-to-beat monitoring, oras intermittently as desired for long term monitoring.

Measuring the instantaneous blood pressure instead of its changerelative to a calibrated baseline measurement means, for example, thatas arterial walls stiffen (due to disease, drug therapy, and/or normalvasculature responses, for example) which increases the PWV, this newPWV value is measured along with any corresponding change in bloodvelocity to produce an updated blood pressure waveform. Additionally, ifthe heart pumps more or less energetically, the blood velocity changesaccordingly, which results in the blood pressure changingproportionately, all else equal. This updated blood velocity measurementat the prevailing PWV (which characterizes the state of the vasculature)corresponds to the updated blood pressure after being scaled by blooddensity. In other words, since there are two measurements made, PWV andblood velocity, and not just PWV alone, a distinct calibration step isnot needed, as the ambiguity of PWV by itself is remedied by adding thesecond measured value of blood velocity. This is of great value overconventional patient NIBP monitoring using PWV alone where typically thecalibration step requires a blood pressure measurement performed byrestricting blood flow, which can be more costly, time consuming, and/oruncomfortable to the patient. In the embodiments discussed below,light-based technology is used to acquire the blood velocity and/or thePWV although other methods of obtaining the PWV and/or the bloodvelocity can alternatively or additionally be used. Further embodimentsimplement various techniques and devices to measure or detectinstantaneous blood velocity. As is described in greater detail below,specific embodiments simplify the task of measuring NIBP withoutsacrificing reliability. Still further, embodiments enable themeasurement of (or at least an estimation of) NIBP without requiringcalibration that relies on a separate means for detecting bloodpressure, which simplifies the treatment and evaluation of the patient.

This disclosure begins with a description of one example of a medicaldevice that may be used in specific embodiments. Next is a discussion ofone embodiment of a sensor for measuring NIBP using ultrasound.Alternative embodiments for sensors which measure NIBP are furtherdiscussed.

FIG. 1 illustrates a non-invasive blood pressure (NIBP) measurementsystem 100 that includes an NIBP sensor 110 and an NIBP module 150. TheNIBP sensor 110 is placed on and/or near a patient to generate andtransmit an NIBP signal 140 to the NIBP module 150. The NIBP signal 140is indicative of the blood velocity and vessel wall motion of thepatient and is processed by the NIBP module 150 to determine/calculatethe blood pressure of the patient. The NIBP measurement system 100, asshown in FIG. 1, allows for the efficient and accurate acquisition ofthe patient's blood pressure.

The NIBP sensor 110 includes a light emitter 120 and a light detector130. Alternatively, the NIBP sensor 110 can include multiple lightemitters 120 and/or light detectors 130. The NIBP sensor 110 is placedon and/or near a patient, such as against the skin of the patient, sothat the light emitter 120 and the light detector 130 are in contactwith or proximally located to the patient. The light emitter 120 emitslight that is transmitted into the tissue of the patient and reflectedfrom various tissues, such as blood vessels, various fluids, such asblood, and/or other features of the patient's anatomy. The reflectedlight is detected by the light detector 130, which outputs the NIBPsignal 140 indicative of the motion of and within the patient'svasculature, the various tissues, fluids and/or other features of thepatient's anatomy.

The light emitter 120 can include a coherent light source 122 and/or anon-coherent light source 124. The coherent light source 122 emitscoherent light which are light waves that are of one phase andfrequency. An example coherent light source 122 is a laser. The coherentlight source 122 can also be a light source that emits non-coherentlight that is then filtered, processed and/or manipulated so that thelight transmitted into the tissues of the patient is coherent. Anon-coherent light source 124 can be a light source that emits light inone or more phases and/or having one or more frequencies and/orwaveforms. Example non-coherent light sources can include light emittingdiodes (LEDs), incandescent, fluorescent, halogen and other non-coherentlight emitting sources.

In an example embodiment, an example non-coherent light source 124 caninclude a narrow or wide bandwidth non-coherent light source. That is,the non-coherent light source 124 can emit light having a relativelynarrow range of variability, or a relatively small or narrow bandwidth.For example, a narrow bandwidth, non-coherent light source can includean LED that emits light across a relatively small range of frequencies.A non-coherent light source, such as an LED, can be used for one or moreoptical interferometry techniques, such as low-coherence interferometry,to acquire and/or determine an instantaneous blood velocity of thepatient.

The light emitted by one or both of a coherent light source 122 and anon-coherent light source 124 can be in a visible, non-visible, or mixedspectrum of light emission. That is, the light emitted by the lightemitter 120 can be within a spectrum of light visible to the human eye,can be in a light spectrum non-visible to the human eye, or a mix oflight including light in both the visible and non-visible spectrum.Example visible light can include colored light, such as visible lighthaving a longer wavelength within the red portion of the visiblespectrum and/or a visible light having a shorter wavelength within theblue/violet portion of the visible spectrum. Non-visible light caninclude short wavelength non-visible light, such as ultraviolet light,and long wavelength non-visible light, such as infrared light.

The one or more light sources 122 and/or 124 of the one or more lightemitters 120 can be selected based on the properties, such aswavelength, frequency, intensity and/or other properties of the lightemitted from the light source 122 and/or 124. In an example embodiment,the light source 122 and/or 124 can be selected based on the wavelengthof light emitted from the light source 122 and/or 124. In human tissues,some wavelengths of light have greater penetrating capabilities, such assome infrared wavelengths, for example, indicating that the lightemitted by the light source 122 and/or 124 travels further into thetissues of the patient before being absorbed and/or reflected. Theincreased penetration depth of some longer wavelength light can increasethe tissue depth in which the NIBP system 100 can accurately determinethe blood pressure of the patient and/or other patient physiologicalproperties, such as blood vessel geometry and/or dynamics.

The light emitter(s) 120 and/or the light sources 122, 124 can beoriented and/or include a directional element to direct the lighttowards the tissues of a patient. In this manner, the emitted light canbe controlled and/or directed along a selected and/or desired pathway.For example, the emitted light can be directed to enter the patienttissues at a specified angle, and/or range of angles, of incidence withrespect to the flowing blood through the vessel. After interacting withthe vessel wall, proximate tissue, and/or flowing blood,reflected/scattered light either reverses direction back towards thesame side the light entered at a second angle back towards the detector(reverse scatter) or continues to the detector on the opposite side ofthe interrogated vessel (forward scatter). The type of scatter isdependent on the position of the detector relative to the emitter.

In an example embodiment, a directional element, such as a diffuserand/or lens can be used in conjunction with the light emitter(s) 120.One or more diffusers can be located between the light emitter(s) 120and the patient to diffuse the emitted light from the light emitter(s)120. Diffusing the light emitted from the light emitter(s) 120 canincrease the area illuminated by the light, such as the area throughwhich the emitted light is transmitted into and/or through the tissuesof the patient. In the example of a coherent 122 and/or a non-coherentlight source, the light emitted by such sources is typically focused toa relatively narrow or small cross-sectional area. Diffusing the emittedcoherent, or non-coherent, light increases the cross-sectional area ofthe emitted light which increases the cross-sectional area of thepatient tissues illuminated by the emitted light. The wider area of thediffused light can increase the likelihood of the emitted lightcontacting and reflecting off of a blood vessel and/or blood therein.Non-diffused light illuminates a smaller cross-section of the patienttissues which can require movement of the NIBP sensor 110 to properlyposition the NIBP sensor 110 so that the light from the light emitter(s)120 interacts with a blood vessel of the patient in order to allow forthe determination, capture and/or calculation of the instantaneous bloodvelocity of the patient.

Additionally, two or more of the light emitter(s) 120 and/or the lightsources 122, 124 can emit light have varying and/or differentproperties. That is, the NIBP sensor 110 can simultaneously and/orsequentially emit light having varying properties, such as varyingintensities, frequencies, wavelengths and/or other light properties.Emitting light having varying and/or different properties can createmultiple NIBP signals that can be processed by the NIBP module 150 todetermine a blood pressure of the patient in a non-invasive manner. Theuse of multiple and/or different light emitter(s) 120 and/or lightsources 122, 124 may assist with error reduction and increasing accuracyof the determined/calculated blood pressure using the light-based NIBPsystem 100.

In an embodiment, an example NIBP sensor can include both a coherentsource 122 and a non-coherent source 124. Light from one or more of thesources 122, 124 can be selectively emitted in a continuous and/orintermittent manner, such as first emitting light from the coherentsource 122 and second from the non-coherent source 124. The two sources122, 124 can be individually disposed on the NIBP sensor 110 in separatelight emitters 120, or can be integrated into a single light emitter120. A dedicated reference path exists between the non-coherent source124 and on or more light detectors 132 a-132 n of the light detector130. Alternatively, each source 122, 124 can be paired with anindividual light detector 130.

The NIBP sensor 110 also includes one or more light detectors 130 thatcan include one or more detectors 132 a, 132 b . . . 132 n, to detectlight, emitted from the one or more light emitters 120, that isreflected from tissues, blood and/or other components of the patient.The light detector(s) 130 can detect one or more properties of theincoming light to generate a signal, such as an NIBP signal (e.g. motionsignal from blood flow or vasculature walls) 140, that can be outputfrom the NIBP sensor 110 to the NIBP module 150 for processing. Exampleproperties of the incoming light that can be detected by the lightdetector(s) 130 can include the frequency, phase change, wavelength,intensity and/or other properties of the incoming light. The NIBP signal140 output from the NIBP sensor 110 to the NIBP module 150 is indicativeof the detected property(s) of the light detected by the lightdetector(s) 130.

One or more light detectors 130 and/or one or more detectors 132 a, 132b . . . 132 n can be distributed and/or arranged on the NIBP sensor 110to detect light reflected from various tissues, fluids and/or otherfeatures of the patient's anatomy. Each of the light detectors 130and/or the detectors 132 a, 132 b . . . 132 n can be associated with oneor more light emitters 120 and/or sources 122, 124. Alternatively, asingle light detector 130, and/or detector 132 a, can be included todetect the reflected light from the patient tissues and/or fluids.

The light detector 130 and/or the detectors 132 a, 132 b . . . 132 n,can be arranged relative to and/or spaced from the light emitter(s) 120and/or light sources 122, 124. The spacing between the emitter and thedetector influences and/or determines the tissue depth from whichreflected light can be detected especially with incoherent or broad bandsources. The reflected light waveform arrives at the detector along areference path (having no significant motion) along with that which isreflected from the patient tissues. The light detector(s) 130, and/orthe detectors 132 a, 132 b . . . 132 n, are positioned and/or sized todetect the reflected light based on the depth of the tissue from whichthe light is reflected. For coherent light, for example, the correlationis periodic so that there is little depth discrimination. For incoherentlight, the depth is highly resolved as the path length between the lightemitter and the light detector along the reference path is the same asthe path length through the tissue because the light waveform has a verysmall correlation length.

The arrangement of the light emitter(s) 120 and/or light sources 122,124 relative to the light detector(s) 130 and/or detectors 132 a, 132 b. . . 132 n can be used to determine depth information based on thedetected reflected light. As the spacing between the emitted light andthe detected light is known based on the arrangement of the emitter anddetector, or components thereof, the depth of the tissue off which theemitted light reflected could be determined, particularly for incoherentsource 124. The depth information can be informative of the depth ofcertain tissue types, such as a blood vessel, and can also be used todetermine the size of tissue features, such as the cross-sectional areaand/or wall thickness of a blood vessel.

In an example embodiment, the light detector 130 can include an array ofdetectors 132 a, 132 b . . . 132 n that are arranged in a gridformation. Each of the detectors 132 a, 132 b . . . 132 n can generate asignal that includes information regarding the positioning of thedetector 132 a, 132 b . . . 132 n within the grid formation. In thismanner, the NIBP signal 140 generated by each detector 132 a, 132 b . .. 132 n includes properties of the detected light and spacinginformation to determine a depth from which the light was reflectedbased on the spacing between the detector 132 a, 132 b . . . 132 n andlight emitter 120.

The NIBP sensor 110 can be a self-contained device or included as a partof another device. For example, both the NIBP sensor 110 and the NIBPmodule 150 can be included in a single device. Alternatively, the NIBPsensor 110 can be fully or partially self-contained and can transmit theNIBP signal 140 to a separate NIBP module 150, such as via a wired orwireless connection. In a fully self-contained example, the NIBP sensor110 can include the necessary hardware to output the NIBP signal 140,such as including a power source for providing the necessary energy tothe light emitter(s) 120 and/or transmit the NIBP signal 140 to the NIBPmodule 150, such as via a wired or wireless connection. In a partiallyself-contained example, the NIBP sensor 110 can include all or a portionof the hardware required to generate and transmit the NIBP signal 140and require input and/or the assistance of another connected device togenerate and/or transmit the NIBP signal 140, such as requiring aconnection to a power source. Such a power source can be included in theNIBP module 150, with a wired or wireless connection between the NIBPsensor 110 and the NIBP module 150 allowing for the transfer of data,such as the NIBP signal 140, and power from a power source of the NIBPmodule 150 or an external power source coupled thereto.

The NIBP sensor 110 can be constructed to allow it to be reusable onmany patients. As part of the reusability, the construction of the NIBPsensor 110 allows the NIBP sensor 110 to be disinfected, cleaned,sterilized or otherwise receive the requisite cleaning necessary for useon multiple patients. The various components, such as the lightemitter(s) 120 and/or the light detector(s) 130 can be protected by acleanable covering that does not distort and/or adversely affect theemission and/or detection of the light through the cleanable covering.In an embodiment, the covering is a film based covering that can beremoved and replaced to maintain a requisite cleanliness or the film canbe a layer of individual films that can be removed individually betweenuses of the NIBP sensor 110 or the covering could be the diffuser/lens.

In another embodiment, the NIBP sensor 110 can be a disposable article,such as a patch, that can be applied to the patient to acquire, processand/or transmit the NIBP signal 140. Both the light emitter(s) 120 andthe light detector(s) 130 can be disposed on the patch and the patch canbe powered by a connection to the NIBP module 150 which can also supplypower to the patch. The transmission of power and/or data can be througha wired connection, such as by a cable, and/or a wireless connection,such as by inductive power coupling and/or wireless data transmission orenergy harvesting technology or by a local battery.

During use, the NIBP sensor 110 is placed on or against a patient toallow the light emitter(s) 120 to transmit light into the patient'stissues and for the light detector(s) 130 to detect the light reflectedtherefrom. The NIBP sensor 110 structure can include a handle or otherfeatures to assist a user with placing and/or restraining the NIBPsensor 110 against the tissues of the patient.

To assist with an extended monitoring of a patient's blood pressureusing the NIBP system 100, the NIBP sensor 110 can be affixed or securedto the patient during the extended monitoring period. During themonitoring period, the NIBP system 100 can acquire the blood pressure ofthe patient selectively and/or regularly. The acquisition of the bloodpressure of the patient can be automatically initiated/triggered, suchas by a predetermined schedule, a triggering event/physiologicalmeasurement and/or by a signal from an external device/system.Additionally, or alternatively, the acquisition of the blood pressure ofthe patient can be manually triggered, such as by a user actuation ofthe NIBP system 100 and/or by a user caused signal from an externaldevice/system. The NIBP sensor 110 can include positioning elements toassist with minimizing motion of the NIBP sensor 110 when placed on apatient. For example, the NIBP sensor 110 can include a cuff, or othergarment or restraint, to constrain the NIBP sensor 110 in a relativeposition on the patient. The band or restraint can be selectivelyreleasable to ease the securement and removal of the NIBP sensor 110from the patient. Alternatively, the NIBP sensor 110 can be adhered to apatient, such as with a temporary adhesive. The NIBP sensor 110 itselfcan have the adhesive pre-applied or the adhesive can be applied by auser to the NIBP sensor 110 or the patient in preparation for affixingthe NIBP sensor 110 to the patient. Additionally, other suitablesecuring means, such as surgical tape and/or elastic bandages, can beused to secure the NIBP sensor 110 to the patient.

The NIBP system 100 also includes a signal processing module 160, acomputing module 170, an optional display 180, an optional communicationmodule 182 and a pulse wave velocity (PWV) module 184. The NIBP module150 can be a separate device from the NIBP sensor 110 or the NIBP module150 and the NIBP sensor 110 can be integrated in, or as a portion of, asingle device, such as another patient monitoring and/or treatmentdevice(s). The NIBP module 150 and the NIBP sensor 110 can becommunicatively coupled to assist with transmitting the NIBP signal 140from the NIBP sensor 110 to the NIBP module 150.

The NIBP module 150 receives the NIBP signal 140 for processing and usein determining/calculating the blood pressure of the patient. The NIBPsignal 140 includes a Doppler signal caused by the reflection of theemitted light off moving components of the patient's tissues whencompared to an intrinsic or extrinsic reference path, namely the flowingred blood cells within a vessel. The light emitted by the lightemitter(s) 120 penetrates or passes through the patient's tissues andreflects from various components thereof, including blood as it flowsthrough a vessel. The light reflected from the moving blood experiencesa frequency shift from the emitted light due to the reflection of thelight from a moving surface of one or more blood cells. The frequency,or Doppler, shift can be processed to determine the instantaneousvelocity (v_(i)), or speed, of the moving blood through the vessel. Thecombination of the calculated/determined instantaneous velocity of thepatient's blood, the PWV of the patient and the essentially universaldensity of blood (ρ) can be used to calculate the instantaneous bloodpressure (P_(i)) of the patient, such as through the use of Equation 1,for example:

P_(i)=ρPWVv_(i)   (Equation 1)

The signal processing module 160 processes the raw data to produce theNIBP signal 140. As part of the signal processing, the signal processingmodule 160 can include amplification 162, filtering 164 and/orconversion 166 of the received signal. The various signal processingprocedures, such as amplification 162, filtering 164 and/oranalog-to-digital conversion 166, can prepare the NIBP signal 140 forprocessing to determine and/or calculate the instantaneous bloodvelocity (v_(i)) of the patient as well as optionally determining and/orcalculating PWV in some examples.

Amplification 162 of the NIBP signal 140 can be performed using alow-noise amplification (LNA) element and/or circuit to amplify the NIBPsignal 140 while minimizing the degradation of the signal-to-noise ratioof the original NIBP signal 140. Amplification 162 can be necessary forprocessing the NIBP signal 140, as the NIBP signal 140 generated by theNIBP sensor 110 can be a low power signal in this example. The amplifiedNIBP signal 140 can then be filtered 164, such as by the use of ananti-alias filtering element and/or circuit, in preparation forconversion 166. The conversion 166 of the amplified and filtered NIBPsignal 140 can convert the analog signal to a digital signal using ananalog-to-digital conversion element and/or circuit. Upon completion ofthe signal processing of the NIBP signal, the NIBP signal 140 can thenbe processed to determine and/or calculate the instantaneous velocity ofthe patient's blood as well as optionally determining and/or calculatingPWV using start-of-the-art means. In a further embodiment, all or aportion of the signal processing of the NIBP signal 140 can be performedat the NIBP sensor 110 prior to transmission of the NIBP signal 140 tothe NIBP module 150. Alternatively, the NIBP signal can be processedwithout the use of one or more of the intervening signal processingsteps.

The NIBP signal 140 is processed or directed, depending on the NIBPsystem 100 configuration, to be analyzed/evaluated by the computingmodule 170 to determine/calculate the instantaneous blood velocity. Theanalysis/evaluation of the NIBP signal 140 can include furtherprocessing, such as additional filtering, such as by a high-pass,low-pass, and/or band-pass filtering element and/or circuit, to isolatethe relevant portion of the NIBP signal for analysis/evaluation.Additionally, the NIBP signal can be decimated if the bandwidth of thesignal is sufficiently low. The Doppler data of the NIBP signal can thenbe scaled to determine the instantaneous blood velocity and/or analyzedfor additional data about the vasculature of the patient, such as thecross-sectional diameter of the vessel as a function of time.Additionally, the Doppler spectrum of the data can be scaled infrequency based on the angle of incidence of the emitted light relativeto the patient tissues/blood flow of interest as well as the anglerelative to the same tissue/blood flow as it reflects to arrive at thedetector. The values of the angles described can be entered by a user,assumed value(s) and/or determined based on vasculature informationincluding the orientation of the vessel.

Alternatively, one or more of the determined/calculated value of theinstantaneous blood velocity and/or one or more vessel dynamics, such asthe cross-sectional diameter, for example, can be transmitted to thecomputing module 170 to determine/calculate the instantaneous bloodpressure of the patient.

The computing module 170 includes a processor 172 and memory 174. Theprocessor 172 can execute various functions and/or programming, such asthat stored in the memory 174 or other storage locations. The variousfunctions can include controlling one or more operations of the NIBPmodule 150 and/or the NIBP sensor 110, such as thedetermination/calculation of an instantaneous blood pressure based onthe instantaneous blood velocity and PWV of a patient. In an embodiment,one or more functions of one or more components of the NIBP system 100can be integrated with the computing module 170, or vice versa. Forexample, one or more components, functions and/or capabilities, orportion thereof, of the signal processing module 160 can be integratedwith and/or performed by the computing module 170, or vice versa.Additionally, one of more functions and/or capabilities, or portionthereof, of the communication module 182 can be integrated with thecomputing module 170. Further, the computing module 170 can includeand/or be connected to an interface, device and/or system for receivinginput from one or more of a user, a device and/or a system remote fromthe NIBP module 150 and/or the NIBP system 100.

The computing module 170 can calculate the instantaneous blood velocityand/or one or more vessel dynamics based on the NIBP signal 140 and canreceive a pulse wave velocity of the patient, such as from the pulsewave velocity module 184. Using these two values and an assumption of arelatively universal blood density, the instantaneous blood pressure ofthe patient can be determined/calculated, such as by using Equation 1above. The instantaneous blood pressure can then be output to a displayand/or communicated to another device and/or system for display and/oruse in one or more device/system functions.

The computing module 170 can also process and/or use the receivedinformation, such as the NIBP signal 140, the PWV and/or otherinformation received by, detected by and/or input to the computingmodule 170 to determine, calculate and/or otherwise process the variousavailable information to assess one or more vascular, hemodynamic,and/or physiological parameters. For example, the computing module 170and/or the NIBP module 150 can process various information, includingthe NIBP signal, to measure one or more vascular parameters, such as thecross-sectional diameter of a vessel, and one or more cardiacperformance parameters. These measurements and/or othermeasurements/assessments based on the information that is able to beprocessed by the computing module 170 and/or the NIBP module 150 canprovide insight into the physiological performance and/or parameters ofa patient monitored by the NIBP system 100. Additionally, theinformation calculated and/or determined by the NIBP system 100 can becommunicated, such as via the communication module 182, to one or moredevices, systems and/or users remote from the NIBP system 100. Thiscommunicated information can be used by one or more of the remotedevices, systems and/or users for various other processes, such aspatient treatment, patient data collection, patient monitoring,post-event reviews/audits, statistical data collection and/or otherprocesses/uses.

The NIBP module 150 can include an optional display 180 that candisplay, or show, information to a user. In an example, the display 180can include indications to a user regarding the NIBP system 100, such asthe detection, or lack thereof, of a blood vessel, an indicated depth ofa detected blood vessel, an instantaneous blood velocity, a pulse wavevelocity and/or a blood pressure value. Alternatively, or additionally,the display 180 can include information regarding the patient, such asan identification, and/or information regarding the NIBP system 100,such as a status of the system 100 and/or one or more components of thesystem 100. Status information of the NIBP system 100 can includemaintenance and/or use related information, such as an indication thatthe NIBP system 100 requires maintenance or instructions to prompt theuser to reposition the NIBP sensor 110 if the NIBP sensor 110 iscurrently not detecting a blood vessel.

The display 180 can include display formats that display actual valuesregarding the displayed information or can display qualities of thedisplayed information. For example, the display 180 can display anactual value of a measured variable and/or the display 180 can displayan indication of the value, such as indicating a position of the valueon a scale indicating one or more ranges associated with qualifiers suchas an acceptable or unacceptable status. The formats of the display 180can include digital formats that alter the display to show informationor can include analog formats that indicate the information on a scaleor other format. In an example, the display and/or an audio element,such as a speaker, can provide a notification/alerts if a value, such asa blood pressure, deviates from a normal value and/or range. Thisalert/notification can inform a user, or others, to the abnormalmeasured and/or determined value of the patient physiological parameter,such as the patient's blood pressure.

In addition to being an output device, the user interface 180 can beand/or can include an input/output means for a user to input informationinto the NIBP module 150 and/or NIBP system 100. For example, the userinterface 180 can include a touchscreen capability to allow the user tointeract with and/or control the NIBP module 150 and/or NIBP system 100.The NIBP module 150 and/or NIBP system 100 can query the user for input,such as for inputting settings and/or other information, and can receivethe requested information via a user input using the input capabilitiesof the display 180. Example user input can include a selection of alight source 122, 124 to use and/or other selection(s) of controllableaspects of the NIBP system 100.

The communication module 182 can provide a communication pathway betweenthe NIBP module 150 and/or the NIBP system 100 via one or more wiredand/or wireless connections. Various communication protocols and/orpathways can be supported by the communication module 182 to allow theNIBP module 150 and/or NIBP system 100 to communicate with remotedevices, systems and/or users. For example, the communication module 182can facilitate communication between the NIBP module 150 and/or the NIBPsystem 100 with one or more remote devices, systems and/or users througha local network and/or internet based connection, such as a Wi-Fi,Bluetooth®, WiGig, and/or other connection/communication protocol,method and/or standard. Communications from the communication module 182can optionally be encrypted and/or transmitted across a securecommunication link established between the communication module 182 andan external device/system. The secure communications can prevent thedissemination of confidential patient information and also can protectthe integrity of the communication from outside influence and/ormanipulation, especially during software upgrades.

The communication module, or other component/system of the NIBP module150, can include user validation functionality. The user validationfunctionality can limit the available features/functionality of the NIBPsystem 100 and/or provide instruction based on the user and theircredentials/validation. For example, a doctor, nurse or healthcareworker can be validated by the user validation functionality as atrained user of the NIBP system. In response, the communication module182 can communicate the user level/validation to the computing module170 to allow, unlock and/or expand one or more functions/features of theNIBP system 100. In another example, the user can be an untrainedindividual and the user validation functionality can validate as such.In response, the communication module 182 can communicate the userlevel/validation to the computing module 170 to restrict one or morefunctions/features of the NIBP system 100. Additionally, the NIBP system100 can provide instructions based on the user level/validation, such asproviding additional instructions to users validated as having a lowertraining/experience level. User credentials/validations can betransmitted/communicated to the communication module 182 via a physicaluser input, such as via a numerical keypad and/or touchscreen, or via awireless input, such as contactless identification card, such as nearfield communication (NFC), and/or other wireless data transmissiondevice/system. The user validation functionality can also includeoptional confirmation of the user credentials/validations by confirmingthe received user credentials/validations with a remote device/system,such as a server, via the communication module 182.

In addition to communication with a remote device, system and/or user,the communication module 182 can support communication between the NIBPmodule 150 and one or more NIBP sensors 110. Communication between theNIBP module 150 and one or more NIBP sensors 110 can be via a wiredand/or a wireless connection. The connection can support thetransmission of data, such as the NIBP signal, from the NIBP sensor 110to the NIBP module 150 and/or the transmission of data, such as commandsto control the light emitter(s) 120, from the NIBP module 150 to theNIBP sensor 110. That is, the connection between the NIBP sensor 110 andthe NIBP module 150 can be a two-way connection to allow thetransmission of data, commands and/or other communication between theNIBP sensor 110 and the NIBP module 150.

Additionally, the communication module 182 can be modular and/orexpandable to allow upgrading and/or replacement of one or morecommunication modules 182. For example, the communication module 182 canfacilitate secured communications between the NIBP module 150 and/or theNIBP system 100. The secure communication network/protocol can requirespecific hardware to allow the NIBP module 150 and/or NIBP system 100 toaccess the secure communication network/protocol. To allow the NIBPmodule 150 and/or NIBP system 100 to access the secure communicationnetwork, the proper communication module 182 can be inserted into and/orotherwise coupled to the NIBP module 150 and/or NIBP system 100.

The NIBP module 150 can include an optional pulse wave velocity module184 that can determine a pulse wave velocity of a patient, receiveinformation related to the pulse wave velocity of the patient and/orconnect to one or more devices to capture the data for use indetermining a pulse wave velocity of the patient. Pulse wave velocity(PWV) is the velocity at which the pressure wave, caused by arterialpulse, propagates through the circulatory system of a patient, or other.Pulse wave velocity information can be sensed by the NIBP system 100and/or another device/system near, or substantially, simultaneously asthe collection of the NIBP signal 140. This near, or substantially,simultaneously acquisition of PWV data and blood velocity data negatesthe need for a calibration step to determine an accurate blood pressureusing Equation 1, for example. Equation 1 is representative of asolution to one of several possible mathematical partial differentialequations describing the physics relating blood pressure, bloodvelocity, and vessel area and diameter. The disclosure can rely on anyof the mathematical equations that relate blood pressure, bloodvelocity, and vessel area and diameter (vessel geometries), such as oneor more constitutive equations described in U.S. patent application Ser.No. 16/103,797, filed Aug. 14, 2018 entitled “CONSTITUTIVE EQUATION FORNON-INVASIVE BLOOD PRESSURE MEASUREMENT SYSTEMS AND METHODS,” which isincorporated by reference herein in its entirety.

The pulse wave velocity received and/or determined by the pulse wavevelocity module 184 and the instantaneous blood velocity informationdetermined by the NIBP system 100, can be used, such as by Equation 1,to determine the instantaneous blood pressure of a patient. PWV data canbe collected using the NIBP system 100, such as through processing theNIBP signal 140, and/or can be received from an external device/systemas a pulse wave velocity signal 142. The pulse wave velocity signal 142can be obtained using various techniques, such as pulse wave Doppler(PWD) and/or continuous wave Doppler (CWD) techniques to obtain rawsignal data that is processed to determine and/or calculate the PWV.Ultrasound and/or light-based systems and/or device can use thetechniques, such as PWD and/or CWD, to collect PWV data for use by theNIBP system 100. Additionally, the PWV and/or the instantaneous bloodvelocity measurements and/or vessel geometry can be used to determineadditional circulatory data, such as vessel information, cardiac outputand/or other measurements or circulatory performance metrics.

FIG. 2 illustrates an example light-based non-invasive blood pressuresystem 200 with a coherent light source. An NIBP sensor 210 is shown,including a light emitter 220, with a coherent light source and a lightdetector 230. The light emitter emits light 222 and 224 through skin 250into deeper tissue 251 containing blood vessel 260. The light detector230 receives reflected light 232 and 234 that is reflected from tissue251 and blood vessel 260. The skin 250 and tissue 251 has a depth 252,or thickness, to the blood vessel 260, which has a vessel diameter 262,a vessel wall thickness 264 and a blood flow 266. The reflected light232, 234 from the various tissues/features of the tissue 251 and bloodvessel 260 is received by the light detector 230 to generate an NIBPsignal that can be processed to determine measurements of thetissues/features, such as an instantaneous blood velocity, which can beused in various calculations to determine one or more physiologicalparameters, such as an instantaneous blood pressure.

In the example shown in FIG. 2, the light emitter 220 includes acoherent light source, such as a laser diode that emits the light 222,224. The coherent light source emits light at a fixed frequency that issufficiently low to penetrate the tissue 251 and/or vessel 260, such asinfrared light. Other coherent light sources capable of emitting lightthat sufficiently penetrates tissues, such as skin 250 and vessel 260,can be used. The maximum depth of penetration of the emitted light, suchas 222, 224, is determined at least in part by the spacing distance 212between the light emitter 220, or light source contained therein, andthe light detector 230, or the light detector therein. Additionally, arelative absorption of the path lengths of the emitted light, such as222, 224, the directivity of the light source of the light emitter 220and/or an angle supporting the greatest reflection of light, at least inpart, influence the maximum depth that the emitted light 222, 224 canpenetrate into the tissue 251, 260.

As the emitted light 222, 224 is transmitted into and through thetissues 251, 260, a portion of the emitted light is absorbed by thetissues 251, 260. This absorption reduces the energy of the lighttransmitting through the tissues 251, 260 so the relative absorption ofthe light along the path lengths of the light emitted, such as 222, 224influences the energy of the reflected light 232, 234 reflected from thetissues 251, 260. The energy of the reflected light 232, 234 needs to besufficient to reach the light detector 230 and/or be detectable by thelight detector 230 to generate an NIBP signal. Therefore, the relativeabsorption of each of the path lengths of the emitted light 222, 224 hasan effect on the maximum depth to which the emitted light 222, 224 canbe transmitted to sufficiently reflect as reflected light 232, 234 andbe detectable by the light detector 230.

The angle of the emitted light, such as 222, 224, relative to thetissues 251, 260 supporting the greatest reflection of light received atthe detector 230 is the “angle of incidence” of the emitted light. Theangle(s) of incidence, among other Doppler contributors, from thetissues 251, 260, results in the reflected light 232, 234 with thegreatest energy and/or is the angle at which the incidence angle of thelight relative to and contacting the tissues 251, 260 is substantiallysimilar to the reflection angle of the light relative to and reflectingfrom the tissues 251, 260 on its way to the detector 230. These twoangles each cause a change in frequency in the signal as perceived bythe detector 230 (between the light emitter and the flowing blood andthe flowing blood and the detector, respectively) and together can beused to calculate the Doppler correction factor.

An angle 256 is the incidence angle of the emitted light 222, 224relative to a normal 254 of the interrogated tissue 251. The angle 256can be based on an orientation of the light source of the light emitter220, such as positioning/orienting the light source to project/emitlight, and/or directing the emitted light, so that it reflects from thetissue at an angle relative to the normal 254 as the light istransmitted towards the flowing blood. The angle 256 can be also bebased on the refraction of the emitted light, such as 222, 224, causedby the difference in propagating characteristics between the materialcovering the source 220 and the tissue it is in contact with, forexample, the index of refraction of 251, 260. The range of angles oflight emitted from the light source can also have an effect on the angle256 of the emitted light entering the tissues 251, 260 from the lightemitter 220 and/or the light source therein.

To determine an instantaneous velocity of the blood flow 266 in thevessel 260, light 224, emitted from the light emitter 220, istransmitted through the tissues 251, 260 to contact the blood flow 266and reflect therefrom, as reflected or scattered light 234. Thereflected light 234 is received by the light detector 230 and has aDoppler frequency, or shift, from the emitted light 224, due to thereflection of the light 234 from a moving fluid, or component thereof,which is the flowing blood 266. In addition to receiving the Dopplershifted reflected light 234, the light detector 230 also receives light232 that is reflected from non-moving tissues, such as skin and tissuebetween the skin and the exterior vessel wall on either or both sides ofthe vessel. The reflected light 232 and 234 are received by the lightdetector 230, and cause a signal to be generated in response to andbased on the detected light 232, 234.

The low frequency AC portion of the reflected light signal, caused byphotodetection of the light 232 and 234 by the light detector 230, isthe difference frequency/Doppler portion of the signal. The DC portionis the sum of incident power of the Doppler shifted signal, caused byphotodetection of the reflected light 234, and the non-shifted signals,caused by photodetection of the reflected light 232. The low-frequencyAC portion of the signal can then be processed to determine the velocityof the blood flow 266 or any vessel wall motion and/or proximate tissueto determine PWV. The Doppler signal energy is typically a distributionof Doppler energy as there are many blood flow contributors of differentspeeds and angles relative to the source and receiver, for example. Thedistribution of Doppler energy is then mapped, either analytically,based upon the geometry of the vasculature with respect to the sourceand receiver and the assumed and/or measured blood velocity profile, orempirically to the correct velocity of 266. The intensity of the DCportion is, in part, related to the presence of a specular reflectionbetween source and detector as it reflects/refracts when it interactswith tissue 251 and vessel 260. The DC portion may be used to detectmovement of vessel wall surfaces, for example, when a pulse travelsthrough the interrogated portion of the vessel.

The response signal generated by the reception/photodetection of lightby the light detector 230 exhibits an amplitude variation at variousdepths due to reflection of the received light from a specularreflection of a surface. This amplitude response variation phenomenoncan be used to determine the depth 252 of the blood vessel 260 andvarious features of the blood vessel 260, such as the vessel diameter262 and the vessel wall thickness 264, for example. The spacing 212between the light emitter 220 and light detector 230 can be varied todetermine the spacing 212 at which the signal response exhibits anincreased amplitude due to the presence of a specular reflection of asurface. The depth 252 of the vessel 260 can be determined based in parton the spacings 212 between the light emitter 220 and the light detector230, where the amplitude response is increased by a specular reflectionof the vessel wall, for example. Further, the diameter 262 of the vessel260 can be estimated by the variance of the spacing 212 between thelight emitter 220 and light detector 230 at one or more places of thevessel 260. Additionally, the vessel wall thickness 264 can be estimatedfrom the signal generated by the light emitter 230, in response to thereceived reflected light 232 and/or 234.

In addition to the amplitude signal, the detector(s) of the lightdetector 230 along the receive path need to be sufficiently sensitive todetect the Doppler shift in the signal caused by the received reflectedlight 232, 234, with the Doppler shifted signal likely to be in the fewkHz to a few MHz range.

FIG. 3 illustrates an example light-based non-invasive blood pressuresystem 300 with a non-coherent light source. An NIBP sensor 310 isshown, including a light emitter 320, containing a non-coherent lightsource, and a light detector 330. The light emitter 320 emits light 322and 324 into tissues, such as tissue 251 and/or blood vessel 260. Thelight detector 330 receives the reflected light 332 and 334 that isreflected from the tissues of 251 and blood vessel 260. The reflectedlight 332, 334 is received by the light detector 330 to generate theNIBP signal that can be processed to determine, or can be used todetermine, one or more physiological parameters, such as a bloodpressure.

In the example of FIG. 3, the non-coherent light source of the lightemitter 320 can be a light emitting diode (LED) light source that emitslight having a narrow bandwidth. That is the non-coherent light sourceof the light emitter 320 exhibits narrow bandwidth, non-coherence.Alternatively, the LED light source could also emit light having a broadbandwidth. Unlike the example of FIG. 2, in which the light source iscoherent and emits light of known and constant properties, thenon-coherent source of the example of FIG. 3 emits light having a rangeof properties, such as a range of frequencies, wavelengths, periods,phases, and/or other light properties/characteristics. The non-coherentlight source has a coherence length, which manifests as a relativelylarge response at detector 330 when the reference and reflected pathsare the same optical length. In the example of a narrow bandwidth,non-coherent source, the coherence length of the emitted light isgreater than the coherence length of light emitted by a non-coherentlight source emitting light having a broader bandwidth. To account forthe coherence length of non-coherent light, the NIBP sensor 310 of FIG.3 includes a reference path 314 that provides a known pathway for lightfrom the light emitter 320 to detector 330.

The reference path 314 determines the depth to which measurements can bemade. The path lengths of the light 322, 324 transmitted through thetissues 251, 260 and back as 332, 334 are limited by the allowable pathlength of reference light along the reference path 314, which is basedon the physical separation between the light source and a detector ofthe light detector 330. In this manner, the longer the path length ofthe reference light along the reference path 314, the longer the pathlength of the light transmission, such as 322, 324, through the tissuesand back as 332 and 334 can be. The depth from which measurements can betaken is therefore limited by the allowable path lengths of the lighttransmissions, such as 322, 324, with reflection 332, 334 from thetissues 251, 260, provided the relative absorption of the lighttransmitting through the tissues is not so great as to prevent thereflected light 332, 334 from being detected by the light detector 330.

Reference light from the non-coherent light source of the light emitter320 radiates underneath the emitter 320 and along the reference path314. The radiated reference light is provided to the detector(s) of thelight detector 330 to be mixed with reflected light 332 and 334. In anexample embodiment, the reference path 314 can be coated and/orstructured so as assist the non-coherent light traveling along thereference path 314 to mix with the reflected light 332, 334. Forexample, the reference path 314 can be coated such that the portions ofthe reference path coating under the light detector 330 acts as aone-way mirror, allowing reflected light, such as 332, 334, to passthrough the reference path 314 and be received by the light detector330, while preventing the radiant reference light along the referencepath 314 from radiating into the tissues, such as 251, 260. Thereference path 314 allows for the mixing of the reflected light 332 andthe reference light. This mixing superimposes the reference lightemitted from the light emitter 320 and the reflected light 332, 334,which is then detected by/at the light detector 330. In this manner, theprocess of low-coherence optical interferometry can be used todetect/determine the Doppler shift caused by the light 334 reflectingfrom the moving blood flow 266 of the vessel 260.

The coherence length of the non-coherent light source determines the“optical slice,” range and/or depth, over which a useful interferometricsignal can be obtained by the detector, or photodetector, of the lightdetector 330. The depth at which the measurement is being made, such asthe depth from which light is reflected, is based on the path lengthbetween the light source and the light detector. The optical slice isthe range, at that depth, from which the measurement is being made, suchas a ± range about that depth. The coherence length of the non-coherentlight determines the breadth of the optical slice or range. In theexample narrow bandwidth, non-coherent light source, the optical sliceis larger than that of a broader bandwidth, non-coherent light sourcedue to the coherence length of the broader bandwidth, non-coherent lightsource being shorter than the coherence length of the narrow bandwidth,non-coherent light source.

An example broader, or wide, bandwidth non-coherent light source caninclude a “white” light source. White light is composed of light havinga wide variance of wavelengths, frequencies and/or otherproperties/characteristics. As such, the coherence length of such lightis relatively short and the optical slice is very thin, on the order ofmicrons. This narrow optical slice can increase the accuracy of depthdetermination since the range, optical slice, is so narrow due to theshort coherence length. As such, the use of a wide bandwidth,non-coherent light source can increase the accuracy of the depthdetermination and/or measurement of various features, such as the depth252 determination of the blood vessel 260, the diameter 262 of thevessel 260, the wall thickness 264 of the blood vessel and/or othertissue measurements.

In the example system 300 shown in FIG. 3, the spacing 212 between thelight emitter 320 and the light detector 330 can be 30 mm, for example,to allow for a penetration depth of the emitted light to be nearly 30 mmdeep into the tissues 251, 260. Other example spacing distances canrange from 10-100 mm.

In the examples of FIGS. 2 and 3, the NIBP sensor 210, 310 can includemultiple light sources emitting light with similar and/or differentproperties. For example, the light emitter can include multiple sourcesemitting light having the same properties, multiple sources emittinglight having different properties, or a mix of light sources. In thismanner, the light emitter and light detector of the NIBP sensor 210, 310can have multiple pairs of light sources and detectors having varyingspacing between them so that physically varying the separation of thelight emitter and light detector is not required to alter the depth ofsensing. Additionally, as described previously, the light emitter220/320 can contain one or more light sources that emit light, such as222/322, 224/324, into the tissue 251 and vessel 260, and the lightdetector 230/330 can contain one or more detectors to detect reflectedlight, such as 232/332, 234/334, from tissues/features of the tissue 251and vessel 260. That is, the light emitter 220/320 can contain multiplelight sources that are arranged to emit light into the tissues 251, 260and the light detector 230/330 can contain multiple detectors, such asphotodiodes, arranged to receive the reflected light. Each of the lightsources of the light emitter 220/320 can be arranged to form a pair witha detector of the light detector 230/330, separated by a spacing 212.With this arrangement of light sources of the light emitter 220/320 anddetectors of the light detector 230/330, multiple spacings 212 betweensource and detector pairs can be achieved. The signals from the one ormore detectors of the light detector 230/330 can be multiplexed andoutput as the NIBP signal for processing to determine one or morephysiological parameters, such as the instantaneous blood velocityand/or PWV.

To assist with locating a vessel, such as 260, the NIBP module and/orthe NIBP sensor can include a manual and/or automatic search algorithmthat can prompt the user to alter the spacing of the NIBP sensor and/orcan activate one or more light sources of the light emitter to provideNIBP signals from various depths. The NIBP signal(s), associated with aparticular light source(s) and/or spacing(s), exhibiting Doppler shiftare indicative of the depth at which the vessel is located. The searchalgorithm can control the activation of the light sources to find theDoppler shifted signal to determine the depth of the vessel, such as260. The light source-detector pair exhibiting the largest magnitude ofthe Doppler response can then be selected for use in determining and/ormeasuring various physiological parameters and/or features.Additionally, differentiation between veins and arteries is possiblebased on the static or dynamic nature of the Doppler signal from each.

In an example embodiment in which the light detector contains multipledetectors, the signal from each of the detectors can be multiplexed toform a single signal, the NIBP signal, or each signal, or groups ofsignals, can be assigned an individual channel for processing. That is,the signal from the NIBP sensor having multiple detectors can be asingle, multiplexed NIBP signal or can be two or more NIBP signalsassigned to individual channels for processing. The use of multiplechannels for processing can increase the acquisition rate of the signaland therefore provide increased temporal resolution of the parametersbeing monitored and/or measured.

In an example embodiment, the light emitter 320 and/or the lightdetector 330 can be integrated with another device and/or system and/orthe necessary light emission and/or detection can be performed byanother device and/or system to generate, or assist with generating, theNIBP signal. For example, the light emitter and/or light detector can beintegrated with a light-based pulse oximetry and/or perfusionsensor/system. The other device and/or system can emit light that can bedetected by the light detector 330 of the NIBP sensor 310, the otherdevice can detect the light emitted by the light emitter 320 of the NIBPsystem 310, or both the light emission and detection of the lightemitter 320 and light detector 330 can be performed by the otherdevice/system, to generate the NIBP signal for processing.

FIG. 4 illustrates an example light-based non-invasive blood pressuresystem 400 that includes an NIBP sensor. The NIBP sensor includes alight emitter 420 and a light detector 430 arranged about one or moretissues. The light emitter 420 emits light 422 and 424 into tissues,such as tissue 250, 251 and/or blood vessel 260. The light detector 430receives the transmitted light 422, which transmits through the tissues,and reflected, or scattered, light 434 that reflects/scatters from theblood flow 266. In response to the received light 434 and 422, the lightdetector 430 generates the NIBP signal that can be processed todetermine, or can be used to determine, one or more physiologicalparameters, such as a blood pressure.

The light emitter 420 and light detector 430 are shown on substantiallyopposite sides of the tissue cross-section of FIG. 4. In otherembodiments, alternative arrangements of the light emitter 420 relativeto the light detector 430 are possible. In these various arrangements,the light detector 430 will receive light transmitted through and/orreflected/scattered from the various tissues, such as 250, 251 and 260.The reflected/scattered light received by the light detector 430 causesthe NIBP signal to be generated, which can then be processed/analyzedfor various calculations/measurements. In an example, thereflected/scattered light 434 from the blood flow 266 exhibits a Dopplerresponse. The Doppler response is part of the generated/output NIBPsignal, from which a velocity of the blood flow 266 can becalculated/measured. The velocity measurement can then be used todetermine a blood pressure. Doppler responses of the vessel wall and/orproximate tissue can be used to detect pressure pulse motion at one ormore places from which pulse wave velocity may be derived.

FIG. 5 illustrates an example non-invasive blood pressure signalgeneration method 500. At 510 coherent light is emitted and/or at 512non-coherent light is emitted, the emitted light is directed into thetissues of a person. The emitted coherent light 510 and/or the emittednon-coherent light 512 can be emitted from one or more light sources ofa light emitter, such as previously described. Thecharacteristics/properties of the emitted light can interact with thetissues to cause localized heating of the tissues and/or the heating ofthe tissues can be caused by the waste heat due to the generation of theemitted light. The heating of the tissues can cause discomfort to aperson associated with the tissues and/or can cause damage to thetissues. To reduce and/or minimize the discomfort and/or damage, theintensity of the emitted light can be controlled and/or the duration oflight exposure can be controlled. Controlling one or both of the lightintensity and the duration of exposure to the light can allow theheating of the tissues to be controlled. For example, a high intensityof light can be emitted for a short duration so as to provide thenecessary intensity to transmit light to a required and/or desired depthinto the tissues while limiting the duration so as not to unduly heatthe tissues exposed to the emitted light.

The light emitted at 510 and/or 512 transmits through the tissues andreflects therefrom. The reflected light is detected at 520, such as by aphotodetector/light detector, with the light detector generating asignal in response with the interaction between the reference and thereflected light. The signal output by the detector(s) is the NIBP signal530. When the light transmitted through the tissues reflects from movingtissues, such as a blood cell of a blood flow through a vessel, thereflected signal has a Doppler shift/frequency that can be detected inthe signal. When the light transmitted through the tissues reflects fromstationary tissues, such as found in the skin or non-moving tissuesoutside the vessel, the reflected signal exhibits little to no Dopplershift due to the reflection from a substantially static tissue. The NIBPsignal generated at 530 can be analyzed to determine the presence of aDoppler shift/frequency, and if such Doppler frequency is present, itcan be analyzed to determine a velocity of the moving tissues, such asthe instantaneous velocity of the blood flow through the vessel or todetect motion of the blood vessel wall and/or proximate tissue. If theNIBP signal generated at 530 is analyzed and there is not an indicationof a Doppler shift/frequency, such as might be caused by the reflectionfrom a moving tissue, then one or more parameters of the light emissionand/or light detection can be altered to cause the emitted light tocontact and reflect from moving tissues, such as the blood flow throughthe vessel, in order to obtain an NIBP signal containing the Dopplershifted signal. The Doppler shifted NIBP signal can be processed, suchas using a method 600 of FIG. 6, to determine one or more physiologicalparameters and/or characteristics of the patient/person.

FIG. 6 illustrates an example non-invasive blood pressure method 600. At610, the NIBP signal is received, such as by an NIBP module from an NIBPsensor. At 620, the NIBP signal can be amplified, optionally, such as bypassing the signal through a low-noise amplifier and/or circuit. TheNIBP signal can then be filtered, optionally, at 630. The filtering at630 can include anti-alias filtering of the NIBP signal and theconversion of the analog NIBP signal to a digital signal, such as by theuse of an analog-to-digital converter (ADC).

As discussed above, the Doppler shift of the NIBP signal is the ACresponse of the NIBP signal, so the NIBP signal can be further filteredat 630 to remove the DC response, in some examples. The removal of theDC response of the NIBP signal can be done using a high pass filter(HPF) and/or a band pass filter (BPF) to remove the portion of thesignal associated with the DC response. If the bandwidth is sufficientlylow, the sample rate of the NIBP signal can be decimated, if requiredand/or desired.

At 640 and/or 642, the NIBP signal can be processed to determine vesseldynamics, such as at 640, and/or to determine an instantaneous bloodvelocity, such as at 642. To determine the instantaneous blood velocityassociated with the Doppler data of the NIBP signal, the Dopplerspectrum of the NIBP signal can also be scaled, as previously described,by correcting the spectrum by the incidence and reflection angles asmeasured with respect to the motion being detected, i.e., the bloodflow. The angle(s) can be value(s) that a user inputs, value(s) that areassumed by the processing of the signal and/or determined from one ormore scans of the vasculature/tissue. The NIBP Doppler data as afunction of depth can be used to determine the cross-section, ordiameter, of the blood vessel as a function of time.

At 650 and/or 652, pulse wave velocity data is determined/received atnear, or substantially, simultaneously as the determination of the bloodvelocity. Substantially simultaneously is at a time recent enough to bethe PWV that would have been measured coincident with blood velocity,which could be some time later. Alternatively, the PWV could be averagedor taken a time separate from the determination of the blood velocity,such as an average of the patient's historical PWV over time (e.g.,minute(s), hour(s), day(s), or even month(s)). While the preference maybe to rely on a PWV that is as temporally near the determination of theblood velocity as reasonably possible, the patient's historical data canalso be used in applications that do not require as much accuracy orprecision, such as fitness testing, non-emergency or non-criticalmedical situations, and the like.

At 650, the pulse wave velocity can be determined, such as from dataand/or measurements received/obtained by the NIBP system, such as by thesensors/system of the NIBP system, including an NIBP sensor and/or NIBPmodule. For example, CWD techniques can be used to determine PWV datausing the light emitter and light detector of the NIBP system.Collection of PWV data can occur nearly, or substantially,simultaneously as the acquisition of the NIBP signal by the NIBP system.In an example, PWV data can also be obtained and/or determined from theNIBP signal. At 652, the pulse wave velocity data needed for furtherprocessing to determine a blood pressure, can be received from anexternal system, device and/or user. Example external systems/device forobtaining the pulse wave velocity can include the use of ultrasoundbased devices/systems, light based devices/systems and/orpressure/motion sensing based devices/systems. The externalsystem/device can capture the PWV data at near, or substantially,simultaneously as the acquisition of the NIBP and/or determination ofthe blood velocity. The near, or substantially, simultaneous acquisitionof the blood velocity and PWV provides the necessary information tocalculate blood pressure, such as by Equation 1, without a calibrationstep. At 654 the PWV data is obtained, from one or both of 650, 652, foruse in determining/calculating the blood pressure.

At 660, the blood pressure of the patient can be calculated and/ordetermined using the pulse wave velocity data from 650, 652 and theinstantaneous blood velocity and/or vessel dynamics data from 640, 642.For example, the instantaneous blood velocity data of 642, the pulsewave velocity data of 652 and the assumed constant density of blood, canbe processed using Equation 1 to determine the blood pressure of thepatient based on the foregoing parameters/measurements.

Additionally, the data derived and/or generated from the NIBP system canbe used to assess various cardiac performance parameters. Using theblood vessel velocity profile and the blood velocity measurement and thevessel diameter and/or area from the NIBP system, the blood volume perunit time can be calculated/determined, including net flow byintegrating over time. The net flow can indicate reverse flow within thecardiac cycle and can also be used in the calculation of various othercardiac performance parameters such as cardiac output and blood volumeflow rate. This and/or other data of the NIBP system, or derivedtherefrom, can be used in conjunction with physiological parameter datafrom other systems and/or devices to monitor, treat and/or evaluate apatient and/or their physiological performance.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be used forrealizing the invention in diverse forms thereof.

1. A blood pressure measurement system for measuring blood pressure in apatient without restricting blood flow, comprising: one or more lightemitters configured to emit light towards blood flowing through a bloodvessel; one or more light detectors configured to: detect lightreflected from one or both of the blood vessel or the surroundingtissue; detect Doppler shifted light reflected from the flowing blood;and generate a reflected light signal based on both the detected lightreflected from the one or both of the blood vessel and the surroundingtissue and the Doppler shifted light reflected from the flowing blood; aprocessor electrically coupled to the one or more light detectors, theprocessor configured to: receive or determine the reflected light signalfrom the one or more light detectors; determine an instantaneous bloodvelocity of the blood flowing through the blood vessel based at least inpart on the reflected light signal received from the one or more lightdetectors; receive pulse wave velocity data for the blood flowingthrough the blood vessel; and determine a blood pressure based at leastin part on the determined instantaneous blood velocity and the receivedpulse wave velocity data.
 2. The blood pressure measurement system ofclaim 1, wherein the one or more light emitters and the one or morelight detectors are integrated into a blood pressure sensor electricallycoupled to the processor.
 3. The blood pressure measurement system ofclaim 2, wherein the processor is also integrated into the bloodpressure sensor.
 4. The blood pressure measurement system of claim 2,wherein the processor is a remote computing device from the bloodpressure sensor and the blood pressure sensor is coupled to theprocessor by either a hard-wired connection or wireless connection. 5.The blood pressure measurement system of claim 2, wherein the bloodpressure sensor is included in a patch that is structured to be affixedto the patient.
 6. The blood pressure measurement system of claim 5,wherein the patch is disposable.
 7. The blood pressure measurementsystem of claim 5, wherein the patch is reusable.
 8. The blood pressuremeasurement system of claim 1, wherein the blood pressure measurement isbeat-to-beat blood pressure.
 9. The blood pressure measurement system ofclaim 1, wherein the one or more light emitters include a coherent lightsource.
 10. The blood pressure measurement system of claim 1, whereinthe one or more light emitters include a non-coherent light source. 11.The blood pressure measurement system of claim 1, wherein at least oneof the one or more light emitters includes a laser diode.
 12. The bloodpressure measurement system of claim 11, wherein the at least one of theone or more light emitters includes multiple laser diodes that are eachconfigured to emit light having different frequencies.
 13. The bloodpressure measurement system of claim 1, wherein at least one of the oneor more light detectors includes a photodiode.
 14. The blood pressuremeasurement system of claim 1, further comprising a pulse wave velocityelement that is configured to detect pulse wave velocity of the pressurewave travelling down the blood vessel.
 15. The blood pressuremeasurement system of claim 14, wherein the pulse wave velocity elementis configured to detect the pulse wave velocity substantiallysimultaneously with the detected light reflected from the one or both ofthe blood vessel or the surrounding tissue or the detected Dopplershifted light.
 16. The blood pressure measurement system of claim 14,wherein the pulse wave velocity element, the one or more light emitters,and the one or more light detectors are integrated into a blood pressuresensor electrically coupled to the processor.
 17. The blood pressuremeasurement system of claim 14, wherein the pulse wave velocity elementis discrete from one or both of the one or more light emitters and theone or more light detectors.
 18. The blood pressure measurement systemof claim 14, wherein the pulse wave velocity element is integrated withthe one or more light detectors, the processor further configured todetermine the pulse wave velocity of the blood flowing through the bloodvessel based at least in part on the reflected light signal receivedfrom the one or more light detectors.
 19. The blood pressure measurementsystem of claim 18, wherein the processor is configured to determine theblood velocity of the blood flowing and the pulse wave velocity of theblood vessel substantially simultaneously.
 20. The blood pressuremeasurement system of claim 14, wherein the processor is furtherconfigured to determine the blood pressure based at least in part on thesubstantially simultaneously determined blood velocity and pulse wavevelocity.
 21. The blood pressure measurement system of claim 14, whereinthe pulse wave velocity element includes one or more of an ultrasound, apressure sensor, a motion sensor, or a high resolution optical sensor.22. The blood pressure measurement system of claim 1, wherein theprocessor is further configured to determine one or more characteristicsof one or both of the blood vessel and the blood flowing through theblood vessel based at least in part on one or both of the detected lightreflected from one or both of the blood vessel or the surrounding tissueor the detected Doppler shifted light reflected from the flowing blood.23. The blood pressure measurement system of claim 22, wherein the oneor more characteristics include one or more of blood vessel depth, bloodvessel diameter, blood vessel wall thickness, or blood vessel wallelasticity.
 24. The blood pressure measurement system of claim 1,further comprising a display electrically coupled to the processor andconfigured to display the blood pressure.
 25. The blood pressuremeasurement system of claim 1, further comprising a communication moduleelectrically coupled to the processor and configured to transmit one ormore of the blood pressure, the instantaneous blood velocity, or thepulse wave velocity to a remote computing device.
 26. The blood pressuremeasurement system of claim 1, further comprising a signal processingmodule configured to one or more of amplify, filter, or digitize thereflected light signal.
 27. The blood pressure measurement system ofclaim 1, wherein the one or more light emitters and the one or morelight detectors are either each paired with respective multiple lightdetectors or multiple light emitters are paired with one of the lightdetectors.
 28. The blood pressure measurement system of claim 1, whereinthe one or more light emitters are spaced apart from the one or morelight detectors a spacing distance, and wherein the spacing distance iseither fixed or variable.